1. Field of the Invention
This invention relates in general to orbital oxidation ditches, and more particularly to apparatus contained therein to improve clarification of waste water circulating in an orbital oxidation ditch.
2. Prior Art
One known method for the clarification of waste water utilizes an orbital oxidation ditch to aerate waste water through the use of vertical turbines as part of the clarification process. This is achieved by the vertical turbine mixing oxygen with the oncoming waste water stream within the vertical turbine. These ditches are generally used with either external clarifiers or intra-channel clarifiers such as the BOAT.RTM.. BOAT.RTM. is a registered trademark to identify an intra-channel clarifier manufactured by United Industries, Inc.
A typical external clarifier ditch configuration is shown in FIG. 1. In this configuration the waste water flowing in the direction indicated by the arrows enters the vertical turbine area which aerates the waste water stream as it flows through the vertical turbine blades. For the desired amount of aeration to occur the vertical turbine must be sized to create a predetermined minimum velocity of the waste water entering the vertical turbine. However as the aerated waste water stream leaves the vertical turbine a portion of the stream known as "backwash" is directed back toward the oncoming waste water stream. This results in a slowing of the velocity of the waste water stream entering the vertical turbine area. Thus to counteract this loss of velocity the vertical turbine must be sized with regard to the radius of its blades, as well as its speed, to accommodate this loss of velocity. Thus because of the effect of the backwash more energy is required to operate the vertical turbine in order to achieve the desired waste water velocity in the ditch.
FIG. 2 illustrates a typical ditch configuration utilizing an intra-channel clarifier. These clarifiers are generally located in a straight section of the ditch near one of the curved sections. A portion of the waste water stream enters the intra-channel clarifier before the waste water enters the vertical turbine. It is important for the efficient operation of the intra-channel clarifier that the turbulence of the waste water entering the intra-channel clarifier be kept to a minimum. The backwash from the vertical turbine creates additional undesirable turbulence at the point that the waste water is to enter the intra-channel clarifier causing a reduction in the efficiency of the intra-channel clarifier.
In either of the two configurations it would be highly desirable if the vertical turbine speed could be reduced as this would not only reduce the energy requirements of the oxidation ditch system, but would allow greater flexibility to meet the required aeration levels as the characteristics of the waste water stream changed.